This invention relates to a temperature sensing circuit generating an output voltage indicative of temperature, the circuit being of the type which includes a source of a substantially constant current, a voltage divider having a first resistor and a second resistor connected in series to the constant current source, a first transistor whose base-collector path and base-emitter path are connected, respectively, parallel to the first and second resistors whereby the output voltage is generated across the collector-emitter path.
From the U.S. Pat. No. 3,916,508 a current supply source of reference voltage is known wherein a first current branch includes in series connection a number of diodes and zener diodes connected in forward direction; and a parallel connected second current branch also including a number of diodes connected in forward direction one after the other and also including an ohmic voltage divider; the reference voltage is kept at the common point of the voltage divider. This prior art circuit generates temperature dependent reference voltages which have either a positive or a negative temperature coefficient. Accordingly this known circuit can be employed not only as a source of constant voltage but also as a voltage generating temperature sensor. However, if a specific temperature coefficient is desirable, this known circuit allows the generation of preset discrete voltage values at the output of the sensor.
Known are also circuit arrangements which deliver a continuously adjustable temperature-dependent output voltage having a positive temperature coefficient only. For example, from the magazine IEEE Journal of Solid State Circuits, Vol. SC-17, No. 6 (December 1982), page 1198, FIG. 3, a circuit is known which delivers an output current which is proportional to temperature in degrees Calsius. For generating this output current, it employs an internal reference voltage having positive temperature coefficients which are proportional to absolute temperature.
From the textbook of H. M. Rein and R. Ranfft "Integrierte Bipolarschaltungen (Halbleiter-Elektronik, Band 13)", Springer-Verlag,1980 page 272 FIG. 5.6 - 1a, a temperature sensor of this kind is known. This temperature sensing circuit which in the literature is frequently described as a "U.sub.BE -amplifier" has a negative temperature coefficient. By varying voltage dividing ratio of a voltage divider connected to its control electrode and at a suitable selection of absolute values of the resistors in the voltage divider, the output voltage and its negative temperature coefficients can be continuously adjusted. In this known circuit, however, the magnitude of the adjustable temperature coefficient is bound to the value of the output voltage (at a fixed reference temperature).